USB any good?

PCI is normally more reliable than USB wireless devices, but not necessarily better signal. A better antenna, a more powerful transmitter, more sensitive receiver are things to look for to improve signal.

And USB devices have more flexibility in positioning at the end of the USB cable instead of being plugged into a slot inside the case.

Try finding place with best signal, higher up usually works better (if it's not on a end of cable, get one, up to 5m). If it still not good enough get a A4 card, cover it in silver foil, fold it at 90deg and place it behind the receiver. Regards, Martin